Dunno about your kid, but for me, here are the reasons I have traditionally hesitated when deciding on getting any replacement furniture for myself (esp office chairs and beds):
1) What if this thing only feels good for 5 minutes in the store (vs how I will ultimately use it) - i.e. the "back pain" issue
2) I don't want to make the wrong call and be stuck with this thing till it breaks + can be replaced
3) I like my current one a lot still. Nothing I've seen has been better